Blade balancer

ABSTRACT

A blade balancer qualitatively determines imbalance of a lawn mower blade. The blade balancer comprises a tube that rotates on precision bearings about a horizontal axis. A sphere is slidingly captured in one end of the tube concentric with the axis of rotation. A spring biases the sphere partially out of the tube. The mounting hole of a lawn mower blade is placed over the sphere, and the lawn mower blade is pushed against the sphere to slide the sphere into the tube inner diameter until the blade contacts an annular magnet secured to the tube and surrounding the sphere. The blade is thus accurately located for rotation about the horizontal axis. Gravity rotates the lawn mower blade, tube, and sphere together to place any unbalanced mass of the blade at a lowermost point under the horizontal axis. In a modified embodiment of the invention, the sphere is replaced by a plug having a cylindrical section that is slidably captured in the tube inner diameter and a conical section. The conical section projects out of the tube to enter the mounting hole of the lawn mower blade.

This is a divisional of application(s) Ser. No. 08/067,082 filed on May26, 1993, now U.S. Pat. No. 5,398,550.

BACKGROUND OF THE INVENTION

1. Field of the Invention. This invention pertains to balancingmachines, and more particularly to apparatus that qualitativelyindicates imbalance in rotatable objects.

2. Description of the Prior Art. Various equipment has been developed todetermine and eliminate mechanical imbalance in rotatable objects. Suchequipment assures that the mass of the object is symmetricallydistributed about its axis of rotation. Failure to correct imbalanceresults in well known detrimental effects to both the rotating objectand to the structure to which the object is mounted.

Rotatable objects are invariably balanced by adding or subtracting massat appropriate locations on the object. For example, it is known to addsmall weights to an object diametrically opposite the location of aneccentric center of mass. Alternately, material may be removed in radialalignment with and on the same side of the axis of rotation as aneccentric center of mass. Numerous balancing machines are in present usefor performing the foregoing balancing procedures.

The capabilities of prior balancing equipment vary considerably. To suitthe requirement of a particular application, some equipment is verysophisticated, having the ability to both measure and correct objectimbalance on an automatic basis. Such equipment is expensive tomanufacture, and skilled personnel are required to operate it. Otherapplications require more modest demands of the balancing machinery. Forexample, some balancing machines are capable of only measuringimbalance, while other machines are capable of only correctingimbalance.

A particularly important application of balancing machines concernsrotatable objects that are long, narrow, and thin. A typical example isa lawn mower blade. Lawn mower blades rotate at very high speeds.Further, in many lawn mowers, the blade acts as the flywheel for theinternal combustion engine that powers the lawn mower. It is thereforevital that the blade be accurately balanced.

In addition to the actual balancing, another very important requirementmust be met in the case of lawn mower blades. The blades are subject tovery hard use, and even abuse, during the normal course of theiroperation. Consequently, the blades must be periodically removed fromthe lawn mowers and serviced. That is in contrast to many rotatableobjects whose balance characteristics do not change with use and so needbe balanced only when they are initially placed into service. When thefrequent servicing factor is considered in light of the relatively lowinitial cost of a lawn mower blade, the requirement arises that lawnmower blades must be balanceable at a very low cost. That is, it is aneconomic necessity that a blade be rebalanced for only a few dollars.Accordingly, low cost equipment is used to service lawn mower blades,and different machines are usually used to determine the amount andlocation of imbalance and to correct the imbalance.

An example of a prior machine for determining the amount and location ofimbalance in a lawn mower blade and the like may be seen in U.S. Pat.No. 2,987,924. In the balancer of that patent, a cylindrical tube havinga cone on one end is mounted on bearings for rotation about a horizontalaxis. A strong magnet is accurately slidable along the cylindrical tube.A mounting hole in the lawn mower blade is centered on the cone, and themagnet is slid along the tube until it contacts and holds the bladefirmly in place with the plane of the blade being perpendicular to thehorizontal axis. If the weights of the two blade ends are unequal, thetube, cone, and blade will rotate under the influence of gravity suchthat the blade heavier end lies under the lighter end. Then the blade ispulled from the balancer and taken to another machine for removal ofmaterial.

A balancing application somewhat related to lawn mower blades concernsindustrial and commercial saw blades. Such blades are very thin and haverelatively large diameters. Their mounting holes are often tapered. U.S.Pat. No. 3,659,463 shows an example of a machine for qualitativelydetermining the imbalance of saw blades.

The balancing machines of the 2,987,924 and 3,659,463 patents have beenin commercial use for many years and have contributed to the balancingof countless lawn mower blades, saw blades, and the like. Nevertheless,they are subject to improvement.

SUMMARY OF THE INVENTION

In accordance with the present invention, a precision blade balancer isprovided that determines imbalance of a rotatable object in a moreeconomical manner than was previously possible. This is accomplished byapparatus that includes a slidable locating plug and a magnet thatcooperate to locate and hold the object for gravity induced rotation.

In one embodiment of the invention, the locating plug is in the form ofa sphere that is slidably captured inside one end of a tube. The secondend of the tube is mounted in very accurate bearings for rotation aboutthe longitudinal axis of a horizontally oriented shaft. The centroid ofthe sphere is coincident with the tube axis of rotation. The sphere isbiased out of the tube first end to a maximum projection therefrom ofapproximately one-third of the sphere diameter. The sphere can bedepressed fully into the tube against the biasing force.

The magnet is annular in shape. It is secured snugly over the tube andgenerally surrounding the sphere. The object to be balanced must be madeof a magnetic material, and it must have a mounting hole generallycoincident with its axis of rotation.

The blade balancer of the invention is used by placing the mounting holeof the object over the sphere. The object is then pushed against thesphere such that the sphere is forced into the tube until the objectcontacts the magnet. The magnet holds the object in place with its axisof rotation concentric with the tube axis of rotation. Upon releasingthe object, the magnet, tube, sphere, and object are free to rotate as aunit about the tube axis of rotation. Gravity acts on the object torotate it to a position whereat any unbalanced mass lies at a lowermostpoint under the axis of rotation. The object can then be pulled from theblade balancer for removal of the excess mass.

In a modified embodiment of the invention, the locating plug is formedas a combined cylinder and cone. The plug is biased to project the coneend thereof out of the tube. The operation of the cylinder and cone plugis generally similar to that of the sphere embodiment. The mounting holeof the object to be balanced is placed over the cone end of the plug.The object and the plug are pushed together against the biasing forceuntil the object contacts and is held in place by the magnet. Uponreleasing the object, it will rotate with the tube, magnet, and plug toplace any unbalanced mass at a lowermost position relative to the restof the object.

The apparatus of the invention enables imbalance of a rotatable objectto be determined with great accuracy but with very low cost. Low initialcost combined with ease of operation results in a highly efficient andproductive balancing machine.

Other advantages, benefits, and features of the present invention willbecome apparent to those skilled in the art upon reading the detaileddescription of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the blade balancer of the presentinvention.

FIG. 2 is a front view of the blade balancer showing a typical objectinitially placed on the blade balancer for balancing.

FIG. 3 is a view similar to FIG. 2, but showing the orientation of anunbalanced object held in place on the blade balancer.

FIG. 4 is a longitudinal cross sectional view of the blade balancer ofthe present invention.

FIG. 5 is a view similar to FIG. 4, but showing an object held in placeon the blade balancer.

FIG. 6 is a view similar to FIG. 4, but showing a modified embodiment ofthe present invention.

FIG. 7 is a view similar to FIG. 5, but showing an object in place onthe blade balancer of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Although the disclosure hereof is detailed and exact to enable thoseskilled in the art to practice the invention, the physical embodimentsherein disclosed merely exemplify the invention, which may be embodiedin other specific structure. The scope of the invention is defined inthe claims appended hereto.

Referring to FIGS. 1-5, a blade balancer 1 is illustrated that includesthe present invention. The blade balancer 1 is particularly useful forqualitatively determining the imbalance of thin planar objects such as alawn mower blade 3. However, it will be understood that the invention isnot limited to use with rectangularly shaped objects.

The blade balancer 1 comprises a base plate 5 that has a hub 7. The baseplate 5 is bored to receive a shaft 9 having a longitudinal axis 10. Theshaft 9 is retained in the base plate by a set screw 11 that passesthrough the base plate hub 7.

Mounted for rotation on the shaft 9 is a balancing unit 13. Lookingespecially at FIG. 4, the balancing unit 13 includes an elongated tube15 having front and back ends 17 and 19, respectively. The tube 15 has afirst inner diameter 21 that extends from the tube back end 19. Thefirst diameter 21 is sized to accept the outer races of a pair of spacedapart precision bearings 23. The inner races of the bearings 23 receivethe shaft 9. Hence, the axis of rotation of the tube coincides with theshaft longitudinal axis 10. A spacer 24 is placed between the innerraces of the two bearings 23, and the bearing inner races are capturedon the shaft by a pair of snap rings 29. The bearings outer races arecaptured between a snap ring 31 and a stepped washer 33. The steppedwasher 33 has a hub 35. The hub 35 has an outer diameter that is pressedinto the tube inner diameter 21.

The tube 15 has a second internal diameter 25 extending from the tubefront end 17. The second inner diameter 25 is concentric with the tubeaxis of rotation 10, and it accepts a sphere 27, such as a hard steelball. To capture the sphere 27 in the tube second diameter, the frontend 17 of the tube is peened over in several places 36 around thecircumference of its junction with the second inner diameter 25. Thesizes of the inner diameter 25 and the sphere 27 are carefullycontrolled so as to enable the sphere to slide along the tube axis ofrotation 10 with minimum radial movement within the inner diameter 25.Consequently, the centroid of the sliding sphere remains concentric withthe tube axis of rotation 10.

The stepped washer 33 has a flat surface 37 surrounded by an annularwall 39. A cone spring 41 seats on the washer surface 37 and bearsagainst the sphere 27. The spring 41 acts to force the sphere out of thetube 15 such that normally approximately one-third of the sphereprojects out of the tube.

Secured on the tube 15 at its front end 17 is an aluminum sleeve 42.Surrounding the aluminum sleeve 42 is an annular permanent magnet 43.The magnet 43 is sandwiched between outer and inner steel bands 45 and47, respectively. Preferably, the front edges 49 of the steel bands 45and 47 overhang the front end 17 of the tube, the front end 51 of thealuminum sleeve 42, and front end 53 of the magnet 43.

In use, the face plate 5 is attached in any suitable manner to a standor post 55 such that the axis 10 of the shaft 9 is horizontal. In FIG.5, reference numeral 59 represents a mounting hole located atsubstantially the axis about which the blade 3 rotates when it is inuse. A person places the blade mounting hole 59 against the sphere 27.He pushes the blade in the direction of arrow 64 (FIG. 5) against thesphere with sufficient force to slide the sphere in the inner diameter25 of the tube 15 against the force of the spring 41. The person pushesthe blade until it contacts the front edges 49 of the steel bands 45 and47. At that point, the magnet 43, acting through the steel bands, holdsthe blade in place with the axis of rotation of the blade mounting holeconcentric with the tube axis of rotation 10. Then the person manuallyrotates the blade, together with the entire balancing unit 13, such thatthe blade is horizontally orientated, FIG. 2. When the person releasesthe blade, the blade and balancing unit will rotate under the influenceof gravity so that one blade end 61 lies lower than the other end 63,FIG. 3, if the end 61 is heavier than the end 63. The anti-frictionqualities of the bearings 23 enable even small amounts of imbalancebetween the blade ends 61 and 63 to cause rotation of the blade and thebalancing unit.

Upon determining that the arm 61 is the heavier, the person removes theblade 3 from the blade balancer 1. That is achieved merely by pullingone blade end 61 or 63 in the direction of arrow 66 away from thebalancing unit 13 to break the magnetic force between the blade and themagnet 43. The entire blade is then taken away from the blade balancerto have material removed from its heavy end 61 by any of a variety ofwell known methods. Then the balance of the blade is rechecked on theblade balancer 1 by repeating the foregoing procedure. When the bladeremains at the horizontal attitude of FIG. 2 after release, thebalancing process is complete.

Turning to FIGS. 6 and 7, a modified blade balancer 65 is depicted. Theblade balancer 65 is generally similar to the blade balancer 1 describedabove, having a shaft 9' with a horizontal axis 10' and a balancing unit68. The balancing unit 68 includes a tube 15' with an axis of rotationthat coincides with the shaft axis 10', precision bearings 23', and astepped washer 33'. The blade balancer 65 also has a magnet 43' withsteel bands 45' and 47' and an aluminum sleeve 42'.

The tube 15' has an inner diameter 67 that is concentric with the tubeaxis of rotation 10. The tube inner diameter 67 slidingly receives alocating plug 69 in the form of a combined cylindrical section 71 andconical section 73. The end of the conical section 73 may be flattenedas at reference numeral 75. The cylindrical section 71 of the locatingplug 69 slides with minimal radial clearance within the tube innerdiameter 67. A spring 77 seats against the stepped washer 33' and biasesthe locating plug out of the tube inner diameter such that the conicalsection projects from the tube end 17'. To capture the locating plug inthe tube, the front end 17' of the tube is peened over in several places79 around the circumference of its junction with the inner diameter 67.

The blade balancer 65 is used in a manner similar to the use of theblade balancer 1 described previously in conjunction with FIGS. 1-5. Aperson places the mounting hole 59' of a lawn mower blade 3' or the likeover the conical section 73 of the locating plug 69. The person pushesthe blade 3' against the plug to slide it in the inner diameter 67 ofthe tube 15' until the blade contacts the bands 45' and 47'. Themagnetic force of the magnet 43' then holds the blade in place. Theperson manually rotates the blade to the horizontal attitude of FIG. 2and releases his hands. Unless the blade is already balanced, the bladeand the balancing unit 68 will rotate to position similar to that ofFIG. 3. The person then grasps the blade by one end and pulls it fromthe blade balancer 65 for metal removal or other servicing.

In summary, the results and advantages of lawn mower blades, saw blades,and the like can now be more fully realized. The blade balancers 1 and65 of the present invention enable any imbalance in a blade to bedetermined quickly, accurately, and at an exceptionally low cost. Thisfavorable result comes from using a spring loaded sphere 27 or otherlocating plug to locate a mounting hole 59 of the blade 3 concentricwith a horizontal axis 10 of rotation of the blade balancer. The bladeis magnetically held to the blade balancer for rotation therewith bygravity about the blade balancer axis of rotation to qualitativelydetermine any imbalance in the blade.

Thus, it is apparent that there has been provided, in accordance withthe invention, a blade balancer that fully satisfies the aims andadvantages set forth above. While the invention has been described inconjunction with specific embodiments thereof, it is evident that manyalternatives, modifications, and variations will be apparent to thoseskilled in the art in light of the foregoing description. Accordingly,it is intended to embrace all such alternatives, modifications, andvariations as fall within the spirit and broad scope of the appendedclaims.

I claim:
 1. A method of balancing a lawn mower blade having a mountinghole therein comprising the steps of:a. providing a stationary shaftthat defines an axis of rotation; b. mounting a tube for rotation on theshaft; c. biasing a locating plug to project out of the tube; d. placingthe blade mounting hole over the locating plug; e. pushing the bladeagainst the locating plug and forcing the locating plug into the tube;f. magnetically holding the blade proximate the tube; and g. rotatingthe blade, locating plug, and tube about the axis of rotation by gravityand determining any imbalance in the blade.
 2. A method of balancing alawn mower blade having a mounting hole therein comprising the stepsof:a. providing a tube; b. biasing a locating plug to project out of thetube; c. placing the blade mounting hole over the locating plug; d.pushing the blade against the locating plug and forcing the locatingplug into the tube; e. magnetically holding the blade proximate thetube; and f. rotating the blade, locating plug, and tube about an axisof rotation by gravity and determining any imbalance in the blade,wherein: i. the step of providing the tube comprises the step ofproviding the tube with an end and with an inner diameter extending fromthe end that is concentric with the axis of rotation; and ii. the stepof biasing the locating plug out of the tube comprises the step ofslidingly capturing the locating plug in the tube inner diameter.
 3. Amethod of balancing a lawn mower blade having a mounting hole thereincomprising the steps of:a. providing a tube; b. biasing a locating plugto project out of the tube; c. placing the blade mounting hole over thelocating plug; d. pushing the blade against the locating plug andforcing the locating plug into the tube; e. magnetically holding theblade proximate the tube; and f. rotating the blade, locating plug, andtube about an axis of rotation by gravity and determining any imbalancein the blade, wherein: i. the step of providing the tube comprises thestep of providing the tube with an end and with an inner diameterextending from the end that is concentric with the axis of rotation; andii. the step of biasing the locating plug out of the tube comprises thesteps of: providing a sphere; and slidably capturing the sphere in thetube inner diameter.
 4. A method of balancing a lawn mower blade havinga mounting hole therein comprising the steps of:a. providing a tube; b.biasing a locating plug to project out of the tube; c. placing the blademounting hole over the locating plug; d. pushing the blade against thelocating plug and forcing the locating plug into the tube; e.magnetically holding the blade proximate the tube; and f. rotating theblade, locating plug, and tube about an axis of rotation by gravity anddetermining any imbalance in the blade, wherein: i. the step ofproviding the tube comprises the step of providing the tube with an endand with an inner diameter that extends from the end that is concentricwith the axis of rotation; and ii. the step of biasing the locating plugout of the tube comprises the steps of: providing a plug having acylindrical section and a conical section; and slidingly capturing theplug cylindrical section in the tube inner diameter and projecting theplug conical section outside the tube.